Question

which of the following statements concerning thoracic volume is true?
multiple choice
in expiration, the thoracic volume increases.
constriction of bronchioles assists breathing.
pressure is directly proportional to volume.
as thoracic volume increases, alveolar pressure (p_{alv}) increases.
as alveolar volume increases, alveolar pressure (p_{alv}) decreases.

Explanation:

• In expiration, the thoracic volume increases: False. During expiration, the thoracic volume decreases as the diaphragm relaxes and the lungs recoil.
• Constriction of bronchioles assists breathing: False. Bronchodilation (not constriction) helps in easier airflow during breathing.
• Pressure is directly proportional to volume: False. According to Boyle's law, pressure is inversely proportional to volume ($P \propto \frac{1}{V}$ when temperature is constant).
• As thoracic volume increases, alveolar pressure ($P_{alv}$) increases: False. When thoracic volume increases (inspiration), alveolar pressure decreases (air flows in as per pressure gradient).
• As alveolar volume increases, alveolar pressure ($P_{alv}$) decreases: True. Based on Boyle's law ($P=\frac{k}{V}$, where $k$ is a constant at a given temperature), when volume ($V$) of alveoli (part of the thoracic cavity in context of breathing) increases, pressure ($P$) decreases.

Answer:

As alveolar volume increases, alveolar pressure ($P_{alv}$) decreases.